Screen material manufacturing method and applications thereof

ABSTRACT

A metal screen material ( 32 ) having a flat side, in particular electroformed screen material, preferably seamless cylindrical screen material, comprises a network of dikes ( 34 ) which are connected to one another by intersections ( 36 ), which dikes ( 34 ) delimit openings ( 30 ). The height of the crossing points ( 36 ) is not equal to the height of the dikes ( 34 ). The metal screen material ( 32 ) or a combination thereof with a perforating screen ( 17 ) can he used as a perforating stencil for the perforation of film material ( 2 ), for example made from plastic material.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of NetherlandsApplication No. 1021907 filed 12 Nov. 2002 and Netherlands ApplicationNo. 1023005 filed 24 Mar. 2003.

BACKGROUND OF THE ART

According to a first aspect, the invention relates to a screen materialmade from metal having a flat side, comprising a network of dykes whichare connected to one another by crossing points, which dykes delimitopenings. More particularly, the invention according to this aspectrelates to electroformed screen material, preferably seamlesscylindrical screen material.

FIELD OF THE INVENTION

Screen material of this type is known in the specialist field and isused for numerous purposes, such as screen-printing, perforating plasticfilms, etc. A perforating method and device are known, for example, fromU.S. Pat. No. 6,024,553.

In this known method for manufacturing perforated plastic films, a thinplastic film is guided over a perforated cylinder, also known as aperforating stencil, and the film is locally exposed to a pressurizedfluid, such as water or air. As a result, the film is locally deformedinto the perforations of the perforated cylinder and is pressed intothem until, the film breaks, so that perforations are formed in the filmat these locations.

The perforating stencil used in this known method comprises a mouldingcylinder having an external moulding surface and an internal securingsurface, and a support cylinder, which bears the moulding cylinder. Asupport structure of this type is often required in order to lengthenthe service life of the stencil, which is adversely affected by thepressurized fluid, such as water. Discharge holes for discharging thefluid extend through the wall of the moulding cylinder. If the supportcylinder covers certain discharge holes, there is a risk of noperforations or insufficient perforations being formed in the film atthese locations. Also, the shape of a perforation which is formed may beadversely affected by fluid which splashes up or flows back. To avoidthese risks, according to the above patent it is proposed to incorporatea fluid-permeable structure, such as a metal screen or mesh, between themoulding cylinder and the support cylinder, the transverse dimensions(width) of the dykes or wires of the fluid-permeable structure beingsmaller than the largest diameter of the generally circular or ovaldischarge holes. All the discharge holes are therefore at leastpartially open, and (partial) blockage of the discharge holes isavoided. The fluid can be successfully drained away and discharged.

In general, it can be stated that a perforating stencil on the one handhas to have a sufficient strength and on the other hand good dischargeof fluid has to be ensured.

The manufacture of a perforating stencil with a layered structure, inaccordance with the above U.S. patent, is complicated, however, onaccount of the need to align the openings in the various layers. This isbecause unaligned openings could give rise to what is known as the Moiréeffect, on account of the presence of regular patterns of openings whichpartially overlap one another. This Moiré effect can give rise to anabsence of perforations or an insufficient number of perforations in theplastic film.

SUMMARY OF THE INVENTION

On account of the abovementioned complexity of the known perforatingstencil, there is a need for alternatives which on the one hand aresufficiently strong and on the other hand offer a good quality ofperforation. It is an object of the invention to satisfy thisrequirement.

Furthermore, the present invention is based on the object of providing ascreen material, in particular for use in the perforation of plasticfilms, in which the risk of the Moiré effect occurring is reduced.

To this end, the invention provides a metal screen material having aflat side, comprising a network of dykes which are connected to oneanother by crossing points, which dykes delimit openings, the thicknessof the crossing points not being equal to the thickness of the dykes.

An important technical aspect of the screen material according to theinvention is that the screen material, which has a flat side, does nothave a uniform thickness (height), but rather the thickness of thecrossing points, i.e. connecting points, of the separate dykes differsfrom that of the dykes themselves. When the screen material according tothe invention is used as a support structure in a perforating stencil,this on the one hand provides a large number of support points for theperforating screen or moulding cylinder. On the other hand, thisstructure ensures that the perforating stencil has a good permeability,since there is sufficient permeability in the plane of the supportingstructure between the dykes and crossing points. The differing height ofthe crossing points with respect to the dykes is only present on oneside in the screen material according to the invention, specifically onthe opposite side from the flat side. In this description, the termscreen material is understood as meaning a thin material, the mainsurfaces of which are referred to as sides, to distinguish them from thethin side edges. The term “flat” means planar, without projecting parts.The screen material may, for example, be in plate form, but ispreferably a seamless cylinder.

It should be noted that screen material based on a woven structure isknown per se, and in this material if desired the threads of the wovenstructure are bound to one another by the application of anelectroformed coating layer. However, a screen material of this typedoes not have any flat sides, since the threads of the woven structurecross one another on each side alternately. As a result of these threadcrossings, the thickness of a screen material of this type is greater atthe location of these crossing points than the thickness of the separatethreads. Examples of screen materials of this type based on a wovenstructure are described, inter alia, in U.S. Pat. Nos. 1,934,643,5,939,172, 5,453,173, 3,759,799, 4,609,518 and the abovementioneddocument U.S. Pat. No. 6,024,553.

In the invention, the screen material is advantageously made from asingle piece, as will become apparent below from the description of amethod used to manufacture it.

According to a preferred embodiment of the screen material according tothe invention, the thickness of the crossing points is greater than thethickness of the dykes, as will be explained in more detail below. Thedifference between the thickness of the crossing points and thethickness of the dykes is preferably in the range from 20-250micrometres, more preferably in the range from 100-200 micrometres.

With regard to the contact surface with a perforating screen above, theapex angle of an elevated crossing point is advantageously less than120°, for example 100° in the case of a height difference of 130micrometres.

The screen material is advantageously tubular, and more particularly thescreen material is in the form of a seamless cylinder, so that theentire circumferential surface may be provided with screen openings,optionally in a regular pattern. The screen material, in particular incylinder form, is preferably obtained electrolytically, as will beexplained below.

The preferably electroformed screen material according to the invention,for use as a support screen in an assembly of support screen andperforating screen, which assembly is suitable for use for theperforation of thin films, advantageously has one or more of thefollowing properties:

A mesh number of 30-80 mesh. By way of example, the openings arearranged in a hexagonal, orthogonal or other regular pattern. With amesh number of less than 30, there is a risk of the support screen notsupporting the perforating screen to a sufficient extent, while with afineness of more than 80 mesh there is a risk of process water used toform perforations in the film by means of water jets beinginsufficiently drained away.

With a view to strength, the overall thickness of the screen material(including elevated sections) is advantageously greater than 600micrometres (typically 900-1000 micrometres). The permeability of thescreen material (optical openness) is advantageously more than 25%(typically 40%-50%).

The metal used for the screen material according to the invention ispreferably nickel.

According to a second aspect, the invention relates to a method forproducing metal screen material having a flat side, comprising a networkof dykes which are connected to one another by crossing points and whichdykes delimit openings, in particular screen material according to theinvention. The method according to the invention comprises at least oneor more growth steps for electrolytically thickening a screen skeletonwith flat sides in an electroplating bath under controlled conditions,in such a manner that in at least one growth step the growth rate of thecrossing points is not equal to the growth rate of the dykes, so that inthe screen material the thickness of the crossing points is not equal tothe thickness of the dykes.

In this method according to the invention, the starting material used isa screen skeleton with two flat sides. A skeleton of this type is a verythin screen material which defines the basic two-dimensional shape ofthe network. A skeleton of this type can be obtained in a manner knownper se, preferably by electroforming on an electrically conductive diewhich is provided with separate insulator islands, for example made fromphotoresist, which correspond to the screen openings which are to beformed. The dykes correspond to the die tracks or parts which are notcovered with insulating material. According to the invention, thisskeleton is subjected to one or more growth steps under controlledprocess conditions. Generally, an incipient height difference betweendykes and crossing points is produced in a first step, and this heightdifference is then enhanced in subsequent steps.

In other words, the screen material is advantageously produced with theaid of a multistage electroforming process. This process comprises:

Phase 1. The deposition of a metal screen skeleton with flat sides, forexample made from nickel, on a die, preferably a cylindrical die.

Phase 2. This phase comprises one or more thickening steps or growthsteps. The conditions of the thickening steps are selected in such a waythat the desired dyke shape and crossing point shape are formed, itbeing possible for the height differences between the dykes and thecrossing points to be either positive or negative, depending on what isdesired or required for the intended application. The growth may takeplace on both sides, in which case, however, the differing growth ratewith regard to the location of dykes and crossing points only occurs onone side. The thickening steps have a selective growth character, whichmanifests itself in electrolytic growth which preferably does not takeplace in the holes but does take place on the dykes and crossing points,i.e. there is scarcely any widening of the dykes or crossing pointscompared to the amount of growth in the thickness direction.

In one of the thickening steps, the dyke shape and the height differenceof a basic shape of the screen material ultimately obtained are defined.During the subsequent step or steps, this basic shape can be grownfurther until the desired final thickness is reached, and the shapeaspects are made more pronounced or enhanced.

The height differences which are formed in the thickening step whichprovides the basic shape are advantageously controlled by one or more ofthe following parameters.

Forced flow of the bath liquid through the screen skeleton. The flowrate of the electrolyte is advantageously in the range from 200-600l/dm² per hour, and is typically 300 l/dm²/hour. If the flow rate of theelectrolyte through the screen material is higher, uncontrolledturbulence occurs, with the result that the locations on the screenskeleton which are exposed to most electrolyte agitation will grow theleast. If the flow rate is low, there will be scarcely any selectivegrowth.

Concentration of brightener. The concentration is advantageously in therange from 200-500 g/l (typically 400 g/l). An excessively highconcentration of the brightener generally results in a brittle deposit.Lowering the brightener content reduces the selective growth character.It is preferable to use a brightener with properties belonging to thefirst and second classes. Examples of brighteners of this type aredescribed in European Patent Application 0 492 731.

A current density of between 5 and 40 A/dm² (typically approximately 15A/dm²).

Another factor which influences the local growth is what is known as theprimary current distribution, which is related to the geometricdistribution of the metal which is already present. Given an identicaldistance between anode and cathode (skeleton), narrow shapes grow to agreater extent than wider shapes.

The invention also relates to the use of the screen material accordingto the invention or the screen material obtained using the methodaccording to the invention for the perforation of film material. Thescreen material according to the invention is advantageously used as asupport screen, but can also be used as a perforating screen.

Furthermore, the invention relates to an assembly of a support screenand a perforating screen, in which the support screen comprises screenmaterial according to the invention or screen material obtained usingthe method according to the invention. This assembly of concentricscreens is also known as a perforating stencil. It is preferable for themesh number of the support screen to be lower than that of theperforating screen.

When two screens with more or less regular patterns of openings areplaced on top of one another, a Moiré effect generally occurs as aresult of interference. This effect may be disruptive in the perforatedproduct, since perforations which it is intended to produce will not beformed or will not completely be formed. With the combination of screensaccording to the invention, this phenomenon is suppressed by the smallcontact area between the elevated crossing points of the support screenand the perforating screen. The ratio of the mesh numbers of the twoscreens also plays a role. It has been found that the Moiré effect fortwo regular patterns is least disruptive if the ratio between two repeatfrequencies of the two patterns is an integer number ±0.5 (1.5, 2.5;3.5, etc.).

This means that in the case of a perforating screen of 100 mesh, thesupport screen preferably has one of the following mesh numbers: 66.6mesh; 40 mesh; 28.6 mesh; 22.2 mesh, etc. The extent to which this Moiréformation is minimized (i.e. no longer perceptible) increases forcoarser support screens. It has been found that the disruptive Moiréeffect is no longer perceptible when a sheet is perforated using a 100mesh perforating screen and a 40 mesh support screen in accordance withthe invention.

The invention also relates to various methods for manufacturing anassembly of a tubular perforating screen and a tubular support screen.

A first method for manufacturing an assembly of a support screen and aperforating screen, in particular cylindrical (seamless) screens,comprises at least one step of shrinking the perforating screen onto thesupport screen.

During the electrolytic growth of screen material, internal stress isbuilt up, as a function, inter alia, of the current intensity, the typeof brightener which is added, the concentration of this brightener, theprocess temperature and the flow rate through the screen material in thedirection of the anode. Subjecting the screen material to a heattreatment, for example in the case of nickel at a temperature of120-220° C. for approx. 1 hour, generally causes shrinkage of the screenmaterial of the order of 0.1%. In the method according to the invention,the shrinkage characteristics of the two screens are used to secure thescreens taut to one another. In this case, it is advantageous for acylindrical support screen to be subjected to a heat treatment atelevated temperature, so that a support screen with a defined outerdiameter (OD) is obtained, and for a cylindrical perforating screen withan inner diameter (ID) which is slightly larger than the outer diameter(OD) of the support screen to be arranged over the support screen, andfor the unit comprising support screen and perforating screen to besubjected to a heat treatment at a temperature which is lower than thetemperature of the heat treatment of the support screen, for asufficient time to shrink the perforating screen onto the supportscreen.

The method according to the invention produces a cylindrical supportscreen with a defined diameter, for example a diameter in the range from200-1000 micrometres, advantageously greater than 600 micrometres. Theprocess conditions, as indicated above, are selected in such a way thatthe stress which is incorporated will result in a shrinkage of 0.1%. Thescreen obtained in this way is subjected to a heat treatment, with theresult that the diameter of the cylinder is reduced through shrinkage.The result is a cylindrical screen material with a defined outerdiameter (OD). A second (outer) screen as perforating screen is producedwith an inner diameter (ID) which is 0.1% larger than the OD of thesupport screen. The two screens are slid over one another and theassembly is subjected to a heat treatment at a temperature which islower than the temperature of the heat treatment of the support screen.During this process step, the outermost screen will shrink in such amanner that it comes to bear taut around the base or support screen. Onaccount of its rigidity, the screen combination obtained in this way hasa longer service life than the outermost perforating screen alone.

Incidentally, it should be noted at this point that it is described inU.S. Pat. No. 6,024,553 that the controlled shrinkage of the startingsleeve for the moulding cylinder can be used to define its desireddiameter with regard to the thickness of the porous structure.

Another method for manufacturing an assembly of a tubular support screenand a tubular perforating screen, in particular cylindrical seamlessscreens, according to the invention comprises at least one step ofarranging a deformed support screen in the perforating screen andrestoring the original shape of the support screen. In a preferredembodiment of this method, to restore the original shape of the supportscreen an inflatable container is placed into the support screen and isthen pressurized. In this method, the ID of the outer screen is inprinciple selected to be equal to the OD of the inner screen. As aresult of the inner screen being pressed into a kidney shape and theinner screen being positioned in the outer screen in this shape and thenbeing returned to its original round shape with the aid of an inflatablecontainer, such as an airbag, a good fit between the screens isobtained. In this case, the inner diameter of the perforating screen mayadvantageously be slightly smaller than the outer diameter of thesupport screen, so that an even tighter fit is obtained. The outerscreen is then under tensile stress.

Yet another method for manufacturing an assembly of a support screen anda perforating screen, in particular cylindrical seamless screens,comprises at least one step of pushing the perforating screen over thesupport screen with the aid of a pressurized fluid. This method forpositioning two screens taut around one another involves filling boththe holes in the inner screen and the holes in the outer screen with anon-permanent agent, for example photoresist. By creating an air cushionbetween the innermost screen and the outermost screen comprising apressurized fluid, such as compressed air, with the aid of a push-onflange, it is possible for the outermost screen to be stretched in sucha manner that it can easily be slid over the inner screen. When thepressure is reduced, the outermost screen shrinks around the innerscreen. If the inner screen is not sufficiently stable and dimensionallyrigid to withstand the compressed air, a sufficiently strong auxiliarycylinder can be introduced into the inner screen during this processstep. After the screens have been pushed over one another, the resist isremoved.

BRIEF DESCRIPTION 0F THE DRAWINGS

The invention is explained below with reference to the appended drawing,in which:

FIGS. 1 and 2 are photographs of a screen material according to theinvention;

FIG. 3 is a photograph of an assembly of a support screen andperforating screen according to the invention;

FIG. 4 shows a diagrammatic representation of the perforation of aplastic film; and

FIG. 5 shows a diagrammatic cross section through an embodiment of anassembly according to the invention.

DETAILED DESCRIPTION EXAMPLE

A 40 mesh hexagonal screen was produced in the following way. The basewas formed by a cylindrical Ni skeleton with flat inner and outer sideswhich was deposited on a die from an electrolytic bath. The thickness ofthe skeleton of 57 micrometres and a permeability of 53% are achieved ata current density of 30 A/dm². A first thickening step took place with aflow rate through the skeleton of 240 l/dm² per hour from the insideoutwards, a current density of 10 A/dm² with a brightener concentrationof 380 g/l. The brightener used was 1-(3-sulphopropyl)quinoline. Theresulting basic shape had a thickness of 270 micrometres, a permeabilityof 50% and a height difference between the crossing points and the dykesof approximately 30 micrometres. The second thickening step took placewith a brightener concentration of 420 g/l, a flow rate of 300 l/dm² perhour and a current density of 15 A/dm². The resulting screen materialhad a thickness of 900 micrometres, a permeability of 45% and a heightdifference between crossing points and dykes of 130 micrometres. Theapex angle of the crossing points was 90-110°. The height differenceswere present on the outer side, while the inner side had remained flat.

FIGS. 1 and 2 show photographs of the resulting screen material, inwhich the dykes are denoted by reference numeral 34, the openings by 30,the crossing points by 36 and the apex angle thereof by 38.

The screen material is preferably used as a support screen for a screenwith a higher mesh number, for example with a mesh number of 100 mesh.For some applications, such as film perforation, it is desirable to usea screen with a mesh number of typically between 60 and 150 mesh. Thesetypes of screen are characterized by a limited stability with regard tothe high forces which are applied to the screen material during thefilm-perforating process, for example vacuum perforation at elevatedtemperatures at which the film is deformable, or water-jet perforationat lower temperatures. Therefore, the open surface area of the supportscreen has to be larger than that of the perforating screen (outerscreen). The elevations and the small apex angle (<120°) of the crossingpoints prevent excessive numbers of holes in the perforating screenbeing completely or partially blocked, which would result in the sheetnot being perforated at the positions of these holes. Cf. FIG. 3, whichshows a photograph of an assembly of a support screen 32 and aperforating screen 17. The perforating screen 17 is supported on thesupport screen 32 at the positions 40 indicated by dark round dots.

FIG. 4 illustrates the perforation of a plastic film using a perforatingstencil. In FIG. 4, a thin plastic film 2, for example made frompolyethylene, is unwound from a stock reel 4 and guided over aperforating stencil 6, where the film is perforated by water jets 8 witha pressure of, for example, 4 bar, from a water jet device 10. Afterperforation, the film 2, which has been provided with perforations 12,is wound up again onto a reel 14. The perforating stencil 6 is providedwith a pattern of continuous openings 16.

FIG. 5 illustrates a cross section through an embodiment of aperforating stencil during operation. Identical components are denotedby identical reference numerals. The stencil 6 comprises anelectroformed nickel moulding cylinder 17 as perforating screen having adiameter of, for example, approximately 30 cm and a wall thickness of600 micrometres, in which there are round openings 16 (mesh number 100)which are delimited by dykes 19. On the inside of the cylinder 17 thereis a support screen 32 provided with openings 30. The openings 30 aredelimited by dykes 34 of the support screen 32. The crossing points 36,which connect dykes 34 to one another, have a greater thickness thanthese dykes 34 themselves. At the location of an opening 16, the film isdeformed under the pressure of a water jet 8 and is pressed into theopening until the film 2 breaks. This results in the formation of aperforation 12 having the form indicated, which is favourable fornumerous absorbent applications, and since the water is easilydischarged via the support screen, this form of perforation is retained.The water which penetrates through is drained away in a suitable way atthe inner circumference of the support screen.

Examples of applications for perforated film include, inter alia,agricultural plastic, absorbent articles, including absorbent productsfor personal care, for example diapers and sanitary towels. Applicationsof this nature make use of the (direction-dependent) permeability of theperforated film.

1. Metal screen material having a flat side without projecting parts,comprising a network of dikes which are connected to one another byintersections, which dikes delimit openings, the height of theintersections not being equal to the height of the dikes only on theside of the screen material opposite to the flat side, wherein theheight of the intersections is greater than the height of the dikes,wherein the difference between the height of the intersections and theheight of the dikes is in the range from 20-250 micrometers, and whereinthe screen material is electroformed.
 2. Screen material according toclaim 1, wherein the difference is in the range from 100-200micrometers.
 3. Screen material according to claim 1, wherein theintersections have an apex angle of less than 120°.
 4. Screen materialaccording to claim 1, wherein the screen material is in the form of aseamless cylinder.
 5. Assembly of a support screen and a perforatingscreen, in which the support screen comprises screen material accordingto claim
 1. 6. Method for perforating film material, wherein the filmmaterial is perforated using an assembly of a support screen and aperforating screen, in which the support screen comprises screenmaterial according to claim
 1. 7. Method for manufacturing metal screenmaterial having a flat side without projecting parts, comprising anetwork of dikes which are connected to one another by intersections,which dikes delimit openings, comprising at least one or more growthsteps for electrolytically thickening a flat screen skeleton in anelectroplating bath under controlled conditions, in such a manner thatin at least one growth step the growth rate of the intersections is notequal to the growth rate of the dikes, so that in the screen materialthe height of the intersections is greater than the height of the dikesonly on the side of the screen material opposite to the flat side. 8.Method according to claim 7, wherein the controlled conditions comprisea forced flow of the bath liquid through the screen skeleton.
 9. Methodaccording to claim 8, wherein the flow rate of the bath liquid is in therange from 200 l/dm² to 600 l/dm².
 10. Method according to claim 7,wherein the bath liquid comprises a brightener in a concentration in therange from 200-500 g/l.
 11. Method according to claim 10, wherein thebath liquid comprises a brightener having properties of the first andsecond classes.
 12. Method according to claim 7, wherein the currentdensity is in the range from 5 to 40 A/dm².
 13. Assembly of a supportscreen and a perforating screen in which the support screen comprisesscreen material obtained using the method according to claim
 7. 14.Method for manufacturing an assembly of a tubular support screen and atubular perforating screen, in particular cylindrical seamless screens,at least comprising a step of shrinking the perforating screen onto thesupport screen, wherein the support screen comprises screen materialhaving a flat side without projecting parts, comprising a network ofdikes which are connected to one another by intersections, which dikesdelimit openings, the height of the intersections being greater than theheight of the dikes only on the side of the screen material opposite tothe flat side.
 15. Method according to claim 14, wherein a cylindricalsupport screen is subjected to a heat treatment at elevated temperature,so that a support screen with a defined outer diameter (OD) is obtained,and in that a cylindrical perforating screen with an inner diameter (ID)which is slightly greater than the outer diameter (OD) of the supportscreen is fitted over the support screen, and the unit comprisingsupport screen and perforating screen is subjected to a heat treatmentat a temperature which is lower than the temperature used for the heattreatment of the support screen, for a sufficient time to shrink theperforating screen onto the support screen.
 16. Method for manufacturingan assembly of a tubular support screen and a tubular perforatingscreen, in particular cylindrical seamless screens, at least comprisinga step of arranging a deformed support screen in the perforating screenand restoring the original shape of the support screen, wherein thesupport screen comprises screen material having a flat side withoutprojecting parts, comprising a network of dikes which are connected toone another by intersections, which dikes delimit openings, the heightof the intersections being greater than the height of the dikes only onthe side of the screen material opposite to the flat side.
 17. Methodaccording to claim 16, wherein to restore the original shape of thesupport screen, an inflatable container is placed into the supportscreen and is then pressurized.
 18. Method according to claim 16,wherein the inner diameter of the perforating screen is slightly smallerthan the outer diameter of the support screen.
 19. Method according toclaim 16, at least comprising a step of arranging a deformed supportscreen in the perforating screen and restoring the original shape of thesupport screen, wherein a support screen obtained using the methodaccording to claim 8 is used, which comprises at least one or moregrowth steps for electrolytically thickening a flat screen skeleton inan electroplating bath under controlled conditions, in such a mannerthat in at least one growth step the growth rate of the intersections isnot equal to the growth rate of the dikes, so that in the screenmaterial the height of the intersections is greater than the height ofthe dikes only on the side of the screen material opposite to the flatside.
 20. Method for manufacturing an assembly of a tubular supportscreen and a tubular perforating screen, in particular cylindricalseamless screens, at least comprising a step of pushing the perforatingscreen over the support screen with the aid of a pressurized fluid,wherein the support screen comprises screen material having a flat sidewithout projecting parts, comprising a network of dikes which areconnected to one another by intersections, which dikes delimit openings,the height of the intersections being greater than the height of thedikes only on the side of the screen material opposite to the flat side.21. Method according to claim 20, at least comprising a step of pushingthe perforating screen over the support screen with the aid of apressurized fluid, wherein a support screen obtained using the methodaccording to claim 8 is used, which comprises at least one or moregrowth steps for electrolytically thickening a flat screen skeleton inan electroplating bath under controlled conditions, in such a mannerthat in at least one growth step the growth rate of the intersections isnot equal to the growth rate of the dikes, so that in the screenmaterial the height of the intersections is greater than the height ofthe dikes only on the side of the screen material opposite to the flatside.